Ytukyg

I have a list which has 3 elements. It is in a while loop and I want to overwrite its values in each iterations. Here is the code:

private List<Integer> loadList = new ArrayList<>(3);

.

.

.

while(counter < 10) {

    loadList.add(0, taskNum);

    loadList.add(1, taskNum);

    loadList.add(2, taskNum);

    .

    .

    .

    counter++;

}

But after running the code I realized that overwriting is not happening and each time the new elements are being added to the end of the list. For example:

At first : a = [1 2 3]

Then: a = [1 2 3 4 5 6] but I want it to be like a = [4 5 6]

So I changed my code to something like this:

loadList = new ArrayList<>(3);

//initializing

loadList.add(0, 0);

loadList.add(1, 0);

loadList.add(2, 0);

while(counter < 10) {

    loadList.set(0, taskNum);

    loadList.set(1, taskNum);

    loadList.set(2, taskNum);

    .

    .

    .

    counter++;

}

But now I'm getting this error:

2018-11-24 13:27:38.298 ERROR [n.f.core.Main] Exception in main

java.lang.IndexOutOfBoundsException: Index: 2, Size: 2

    at java.util.ArrayList.rangeCheck(ArrayList.java:657) ~[na:1.8.0_151]

    at java.util.ArrayList.set(ArrayList.java:448) ~[na:1.8.0_151]

    at net.floodlightcontroller.mactracker.Mactracker.paramInit(Mactracker.java:137) ~[floodlight.jar:1.2-SNAPSHOT]

    at net.floodlightcontroller.mactracker.Mactracker.init(Mactracker.java:205) ~[floodlight.jar:1.2-SNAPSHOT]

    at net.floodlightcontroller.core.module.FloodlightModuleLoader.initModules(FloodlightModuleLoader.java:460) ~[floodlight.jar:1.2-SNAPSHOT]

    at net.floodlightcontroller.core.module.FloodlightModuleLoader.loadModulesFromList(FloodlightModuleLoader.java:295) ~[floodlight.jar:1.2-SNAPSHOT]

    at net.floodlightcontroller.core.module.FloodlightModuleLoader.loadModulesFromConfig(FloodlightModuleLoader.java:235) ~[floodlight.jar:1.2-SNAPSHOT]

    at net.floodlightcontroller.core.Main.main(Main.java:61) ~[floodlight.jar:1.2-SNAPSHOT]

What's wrong and how can I solve this problem?

With this line:

loadList = new ArrayList<>(3);

you defined that the initial capacity of the list is 3.

Now you can add as many items as you want not only 3.

But still your list is empty.

You cannot use:

loadList.set(2, taskNum);

if there is no item in the 3d position.
set(position, item) is valid only if there is already an item at position.

So use add(item) to add new items at the end of the list

and set(position, item) to replace the item that is already in the list at position.

You can also use add(position, item) to insert a new item at position, and shift the items from this position to the right.

You are getting the IndexOutOfBoundsException as you are trying to set value at an index which is greater than the size of the list.

loadList.add(0, 0);

loadList.add(1, 0);

loadList.set(2, 0); <--------------- You will get IndexOutOfBound here

As List#set method throws an exception when if the index is out of range(index < 0 || index > size(). Use loadList.add(2, 0), instead of loadList.set(2, 0); will solve your issue.

When you initializing like this,

loadList.add(0, 0);

loadList.add(1, 0);

loadList.set(2, 0); <--- here you are setting instead of adding the value :)

It should be changed to,

loadList.add(0, 0);

loadList.add(1, 0);

loadList.add(2, 0);

you are getting IndexOutOfBoundsException because you set the object at the particular index which is not defined yet.

loadList = new ArrayList<>(3); menas your arryList have initial capacity 3.

first you have to add element at positions then set the elements. try this

loadList.add(0, 0);

loadList.add(1, 0);

loadList.add(2, 0);

An Example, That will give you an Idea.

List alist = new ArrayList();

    alist.add("1");

    alist.add("2");

    alist.add("3");

    int j=4;

    for(int i=0;i<=2;i++){

        System.out.println("alist.get(0)"+alist.get(0));

        System.out.println("alist.get(1)"+alist.get(1));

        System.out.println("alist.get(2)"+alist.get(2)+"n");

        alist.add(0, j++);

        alist.add(1, j++);

        alist.add(2, j++);

    }